<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .grid {
            display: grid;
            grid-template-columns: 1fr 1fr 1fr;
            grid-template-rows: 1fr 1fr;
        }
        .grid > div {
            padding: 2em;
            border: 1px solid #000;
        }
        div.a, div.b, div.c {
            border-top-width: 2px;
        }
        div.d, div.e, div.f {
            border-bottom-width: 2px;
        }
        div.a, div.d {
            border-left-width: 2px;
        }
        div.c, div.f {
            border-right-width: 2px;
        }
        
    </style>
</head>
<body>
    <h1>网格剖析</h1>
    <h2>网格线</h2>
    <div class="grid">
        <div class="a"></div>
        <div class="b" style="border-right: 3px solid red;"></div>
        <div class="c" style="border-left: 3px solid red;"></div>
        <div class="d"></div>
        <div class="e" style="border-right: 3px solid red;"></div>
        <div class="f" style="border-left: 3px solid red;"></div>
    </div>
    <h2>网格轨道</h2>
    <div class="grid">
        <div class="a" style="background-color: red;"></div>
        <div class="b" style="background-color: red;"></div>
        <div class="c" style="background-color: red;"></div>
        <div class="d"></div>
        <div class="e"></div>
        <div class="f"></div>
    </div>
    <h2>网格单元</h2>
    <div class="grid">
        <div class="a"></div>
        <div class="b"></div>
        <div class="c"></div>
        <div class="d"></div>
        <div class="e" style="background-color: red;"></div>
        <div class="f"></div>
    </div>
    <h2>网格区域</h2>
    <div class="grid">
        <div class="a"></div>
        <div class="b" style="background-color: red;"></div>
        <div class="c" style="background-color: red;"></div>
        <div class="d"></div>
        <div class="e" style="background-color: red;"></div>
        <div class="f" style="background-color: red;"></div>
    </div>
</body>
</html>